With the recent trend of increasing the size of liquid crystal displays, their applications are expanding from personal devices such as mobile phones or laptop computers to home appliances such as wall-mountable TVs. Thus, liquid crystal displays are required to have high definition, high quality, and wide viewing angles. In particular, because thin film transistor-liquid crystal displays (TFT-LCDs) driven by TFTs allow respective pixels to independently operate, the response rate of liquid crystals becomes very high, making it possible to achieve high-definition video images. Accordingly, TFT-LCDs have a variety of applications.
In order for liquid crystals of TFT-LCDs to function as an optical switch, liquid crystals have to be initially aligned in a predetermined direction on a TFT layer located at the innermost position of a display cell. To this end, a liquid crystal alignment layer is utilized. Particularly, photo-alignment methods for orienting a liquid crystal alignment layer by light such as UV are being broadly reviewed these days.
Typically for such photo-alignment, a photo-alignment layer containing a photo-alignment polymer having a photoreactive group is formed under a liquid crystal layer, and then irradiated with linearly polarized UV light so that a photoreaction takes place. As a result, photo-alignment in which the backbone of the photo-alignment polymer is arranged in a predetermined direction occurs, and the alignment layer thus optically aligned has an influence on aligning liquid crystals contained in the liquid crystal layer located thereon.
A typical example of the photo-alignment polymer includes a cyclic olefin-based photo-alignment polymer which is disclosed in Korean Patent No. 0789247, 0671753, or 0982394 by the present inventors. The cyclic olefin-based photo-alignment polymer may exhibit excellent photoreactivity, photo-alignability, and alignment rate as well as superior thermal stability by the cyclic olefin-based backbone structure thereof, and thereby is preferably able to serve as a photo-alignment polymer.
However, the case where the cyclic olefin-based photo-alignment polymer and a photo-alignment layer including the same are applied to a liquid crystal cell to achieve liquid crystal alignment is problematic because an afterimage may be generated or a voltage holding ratio may decrease due to non-hardening of the photoreactive group or the backbone of the photo-alignment polymer which has not yet undergone photoreaction and photo-alignment.